Water-swellable polymers are well-known. There is now the class of "super-absorbent" polymers derived from, for example, (meth)acrylic monomers. They may be provided in the form of flakes or beads which can absorb water and swell by a very large factor, to give swollen beads. Such materials are used in disposable nappies.
If the monomers are polymerized to form long chains and the chains are simply mixed with one another, then, depending upon the monomer and the chain length, the polymer is often water-soluble. If, however, the chains are cross-linked to one another, then the resulting mass is insoluble but may still absorb large quantities of water to form a gel.
In the context of animal feeds, it is known, for example from U.S. Pat. No. 3,957,973, to administer soluble polyacrylamide to pigs. The effect is said to be increased food residence time, which prevents gastric ulcers and pica.
FR-A-2,074,603 discloses the use of a wide variety of polymeric substances in an animal's feed to lower the blood cholesterol level of the animal. This prior teaching is apparently applicable to all warm-blooded animals but is especially useful in the context of chickens and pigs. The polymer may be soluble or insoluble in water.